Soybean is an important source of protein for humans and animals, both in its unprocessed and processed form. Soybeans provide a good source of low-cost protein and have become an important world commodity because they are ubiquitous, have unique chemical composition, good nutritional value, versatile uses, and functional health benefits. Yet, less than about 5% of the soybean protein available is used for food, but this percentage is likely to grow. One of the main bodies of research in recent years has focused on studying individual storage proteins (such as glycinin, β-conglycinin and trypsin inhibitors) and relating them to industrially important functional properties and functional health benefits. In spite of this extensive research these individual proteins or enriched fractions thereof are not widely available at competitive costs.
Soy protein (i.e. protein obtained from soybeans) also contains antinutritional factors, which prevent uptake of nutrients in food. In particular, trypsin inhibitors (TIs) are proteins found among the many soy proteins which inhibits the activity of trypsin (a serine protease enzyme present in the digestive system which hydrolyses proteins). Thus, despite the beneficial functionality of these proteins in other applications, if used as part of a food or animal feed ingredient these proteins will interfere negatively with the digestive enzyme system and may lead to malnutrition and disease.
Particular efforts have therefore been made to reduce the activity of the trypsin inhibitor proteins naturally found in soy protein. A common method is simply to heat the soy protein, which denatures/destroys the trypsin inhibitor proteins. However, this technique also destroys or denatures other proteins in the soy protein, reducing their protein functions (e.g. gel-formation, fat-binding or emulsification). Proteins containing lysine are particularly heat-sensitive. Heating can also reduce the water-solubility of the soy protein.
An alternative to heating the soy protein to destroy the trypsin inhibitor (TI) protein is to separate the trypsin inhibitor (TI) protein from the remainder of the soy protein. This technique has the advantages of avoiding heat, and can also provide isolated trypsin inhibitor (TI) protein (which itself can be a useful medicinal product).
Research efforts have therefore focused on purification of soy protein to isolate the trypsin inhibitor (TI) protein contained therein. Bajpai et al. (Food Chemistry, 89 (2005), 497-501) discuss the use of immobilized metal affinity chromatography for binding trypsin inhibitor and soybean lectins.
WO2011/082358, WO2011/082359 and WO2011/082360 all concern various aspects of isolating and purifying trypsin inhibitor from soy protein.